#include<iostream>
#include<string>
using namespace std;
int st[30];
int n;
string s;
int main()
{
	cin >> n >> s;
	for (int i = 0; i < s.size(); i++) {
		if (s[i] >= 'A' && s[i] <= 'Z') {
			s[i] += 32;
		}
	}
	for (int i = 0; i < s.size(); i++) {
		int x = s[i] - 'a' + 1;
		st[x]++;
	}
	bool flag = 0;
	for (int i = 1; i <= 26; i++) {
		if (!st[i]) {
			flag = 1;
			break;
		}
	}
	if (!flag)cout << "YES" << endl;
	else cout << "NO" << endl;
	return 0;
}